Fully automated climate systems in vehicles are commonly used in vehicles. Originally such climate systems used single or multiple temperature sensors sensing the temperature in the cabin and regulated the airflow in dependence of the temperature measured by said sensors. However, the influence of the radiation of the sun is not adequately compensated for when using only a temperature sensor. Therefore it has been suggested to make use of radiation sensors, which measures the impact of the sun. Further improvements have resulted in sensors, which identifies the position of the sun in relation to the vehicle in order to further improve the regulation of the climate unit. Such sensors are known from inter alia WO 90/07102, U.S. Pat. No. 5,337,802, U.S. Pat. 5,553,775 and EP 852 189. The sensor elements described in these documents all include multiple sensor elements arranged in a housing, where said sensor elements are sensitive to light. The sensor elements are arranged at different geometrical positions of the sensor housing, whereby a sensitivity of the direction of a light source in relation to the sensor can be established. The sensors preferably also include shading elements, which prevent light from reaching one of the sensor elements when impinging from certain positions. By measuring the difference in altitude of the output signal from each of the sensor elements, an estimate of the position of the light source in relation to the sensor is calculated.
A typical response from a prior art sensor having two sensor elements is shown in FIG. 1. The sensor in the example includes a first and second sensing elements positioned in a housing in a manner such that light is blocked from reaching one of the sensor elements if impinging from a first direction and the light is blocked from reaching the other sensor element if impinging from a second opposite direction. A first left curve corresponds to the output signal produced by the first sensor element and a second right curve is produced by the second sensor element. The curves are overlapped in a small region corresponding mainly to a position where the light source impinges vertically on the sensor element. The magnitude of the signals each has a peak value outside side overlapping region and thereafter are steeply reduced to a small fractional value of said peak value. A problem with the sensor type producing such an output signal is that the position of the light source cannot be determined with accuracy outside the overlapping region. It is true that the output signal outside the overlapping interval has a magnitude dependent on the position, however, it is not possible to judge whether a small output signal is dependent on the position of the sun or if it depends on the intensity of the sun. In order to discriminate between these two variables it is necessary to have output signals from both sensor elements.
A typical response from a prior art sensor having a single sensor element is shown in FIG. 2. The output at low angles are typically low in relation to the output from vertically impinging radiation. Since heating problems in car interiors are mostly occurring at impinging angles of about 30–80°, this type of sensor does not conform well for the purpose of detecting a heating effect. Generally, in order to detect the magnitude of the flux of the optical radiation it would be advantageous to have a sensor that has a response from different impinging angles which is as flat as possible. In the event a totally flat output could be generated the output would directly indicate the magnitude of the flux of the optical radiation.